The invention concerns a roller hearth furnace for heating and/or temperature equalization of continuously cast products, especially those made of steel or steel materials, which are cut to lengths that fit the furnace and are then conveyed into and out of the furnace through the furnace chamber on rollers, and a method for using the roller hearth furnace upstream of a hot strip finishing train, in which the hot strip is subjected, among other operations, to rolling, cooling, and coiling into coils in a coiling station.
Roller hearth furnaces of this type are very long and are associated with thermal losses. In addition, due to the long time the continuously cast products lie on the rollers, these roller hearth furnaces cause impressions on the underside of the products as a result of scale caked on the product, and this later leads, during the rolling process, to reduced quality of the rolled product, especially rolled strip.
A roller hearth furnace of this type installed upstream of a hot strip finishing train is described, for example, in DE 44 11 216 A1. This furnace has stationary and traveling hearths, on whose refractory lining the pieces of material to be heated are laid. Sloping depressions are incorporated in the refractory lining to cause the pieces of material to be heated from below and to help remove scale. The scale is removed through travel grooves between the hearths and through scale drop shafts.
In the case of hearths formed by rollers, although the removal of scale is more favorable when the spaces between the rollers are short, residual pieces of scale are pressed into the strand material by the weight of heavy continuously cast products, such as cut lengths of slab, and cause the aforementioned surface defects, which, as described above, persist in the finished product. A traveling hearth equipped with rollers is disclosed, for example, by EP 0 361 057 B1. However, a design of this type results in an extremely complicated structure as a roller hearth and traveling hearth system comprising conveying rollers, which are supported outside the furnace chamber and can be moved into and out of spaces of the traveling hearth through openings in the side walls of the furnace. This results in large heat losses and low thermal efficiency.
Roller hearth furnaces for heating and/or temperature equalization of continuously cast products are known from the documents IT 1 236 130 B, EP 0 264 459 A1, EP 0 353 487 A1, WO 94/18 514 A and DE 35 25 457 A1. These roller hearth furnaces do not allow any change in the thermal efficiency.